Airports have played down the potential impact as Border Agency staff walk out on strike today.
Heathrow has claimed it has enough volunteers to ensure minimal disruption while Gatwick said travellers may experience “some delays” at immigration.
The strike over pensions is part of a wider public services day of industrial action but comes amid rows over Border Agency manning at UK airport, particularly Heathrow.
The government has come under pressure after delays of up to three hours were recorded at Heathrow in recent weeks.
A statement from the operator of Gatwick Airport said: “The Border Force has put appropriate contingency measures in place for today’s strike action to ensure in-bound passengers pass through immigration with as minimal disruption as possible.
“Gatwick Airport has additional staff and volunteers on hand throughout the day in both terminals to assist Border Force colleagues and passengers. Our focus remains on minimising any potential disruption and ensuring our arriving passengers can get through the airport as quickly as possible.
“Gatwick is operating a normal flight schedule today and, at present, passengers are passing through immigration as normal without delays. We will continue provide updates to our passengers throughout the day so they are kept informed of the situation.”
Gatwick is due to handle 265 inbound flights today of which are inbound EU flights and 55 are inbound Non-EU flights. There will be around 43,000 arriving passengers in all.
Heathrow said it has had assurances from the Border Agency that enough volunteers have come forward to man immigration despite the action by the Public and Commercial Services Union’s 13,000 members.
Immigration Minister Damian Green told the London Evening Standard: “This strike is completely unnecessary and we believe the public will find it unacceptable if unions push ahead.
“The security of the UK border is of the utmost importance and we will use contingency plans to ensure we minimise any disruption caused by planned union action. We are preparing to use our trained pool of contingency staff and MOD police to boost staffing levels at ports and airports around the UK.”